The present invention relates to methods and apparatus for cardiac treatment generally, and particularly to methods and apparatus for improvement of heart function following myocardial infarction and other ischemic heart conditions.
Heart disease or heart failure following myocardial infarction is still the major cause of death in the western world. The mature heart muscle (myocardium) cells of mammals are those that reach their last stage of differentiation and, therefore, are considered unable to undergo proliferation (see P. P. Rumynastev, Growth and Hyperplasia of Cardiac Muscle Cells, B. M. Carlson, ed., Harwood, New York, 1991, pp. 3-68). Thus, the myocardium may be afflicted with hypertrophy (increase in cell mass and not cell number) due to mechanical stress or ischemia (inadequate oxygen supply to the cells). Following ischemia, due to occlusion of blood supply to the cells during myocardial infarction (MI), irreversible, physiological changes occur in the cells, which degenerate and are replaced by non-contracting scar tissue (infarcted zone) with time (see M. C. Fishbein, M. B. McLean et al., Experimental myocardial infarction in the rat, Am. J. Pathol. 90: 57-70, 1978).
In particular, cells of the myocardium traumatized by ischemia enter a toxic ischemic cascade resulting in a number of damaging processes to the cells, such as membrane breakdown, mitochondrial disruption, enhanced proteolysis, etc., mainly as the result of unbalanced rates of energy production and consumption. Under conditions of poor oxygen availability, an anaerobic glycolytic pathway replaces the aerobic metabolism as the primary source of adenosine triphosphate (ATP), facilitating cell survival. The anaerobic glycolytic metabolism and related anaerobic cell survival, however, is a short-lived mechanism, as this natural up-regulation of glycosis is stopped by the accumulation of lactate, which inhibits the key glycolytic enzyme phosphofructokinase (PFK) (see E. Hofiann, The significance of phosphofructokinase to the regulation of carbohydrate metabolism, Rev. Physiol. Biochem. Pharmacol. 75: 2-68, 1976).
Current clinical treatments of acute MI include thrombolytic treatment (W. Ganz, N. Buchbinder, H. Marcus et al., Intracoronary thrombolysis involving myocardial infarction, Am. Heart 101: 4-10, 1983); PTCA (coronary angioplasty) performed on occluded arteries (A. R Gruentzig et al., Long-term follow-up after percutaneous transmural coronary angioplasty, N. Engl. J. Med. 316: 1127-32, 1987); and also bypass surgery as near as possible to the occurrence of the MI (G. M. Fitzgibon, A. J. Leach, H. P. Kafka et al, Coronary bypass graft fate: long-term angiographic study, J. Am. Coll. Cardiol. 17: 1075-80, 1991). These procedures are expensive, demand very highly qualified personnel and physicians, and are not always practically possible in health care. Moreover, these methods endeavor to alter the consequences of the irreversible ischemic injury that occurs in the cells rather than inhibit such consequences. It should be mentioned that even with qualified personnel and first-rate treatment, the above procedures are not always successful.
Several attempts have been made in the past to reduce the infarcted area in the myocardium following induction of MI in experimental animals. These include the use of corticosteroids, various antioxidant agents, and chemical agents for prolonging anaerobic cell survival.
Exogenous fructose-1,6-diphosphate (FDP) was found to bypass the PFK block and restore anaerobic ATP and creatine phosphate (CP) production (see A. K. Markov, N. C. Oglethorpe, et al., Hemodynamic electrocardiographic and metabolic effects of fructose diphosphate on acute myocardial ischemia, Am. Heart J. 100: 639-646, 1980). In experiments performed on animals, FDP was found to improve hemodynamic parameters, reduce arrhythmias and infarct size, and increase survival rate. (See A. K. Markov, N. C. Oglethorpe, et al., op. cit., and J. W. Starnes, K. S. Seiler, et al., Fructose-1,6-diphosphate improves efficiency of work in isolated perfused rat heart, Am. J. Physiol. 262: M380-M384, 1992. All of these articles are incorporated herein by reference.)
Ischemic cardiac tissues may have their blood supply restored, using various treatments known in the art, such as coronary angioplasty. In the course of such a treatment, the ischemic tissue may be rapidly reperfused with blood. Such rapid reperfusion has been shown, at least in some cases, to result in post-reperfusion injury, i.e., damage induced by the reperfusion per se. The injury may be caused, inter alia, by superoxides formed within the tissue due to a sharp increase in oxygen supply following the reperfusion procedure. Superoxides are highly-reactive, toxic free radical substances, which undergo detrimental, undesirable reactions with organic and inorganic cellular substances. Indigenous and/or exogenous antioxidants alleviate the toxic effect of the superoxides by either preventing their formation or scavenging the free radicals immediately upon formation. Use of exogenous free radicals scavengers for alleviation of post-reperfusion injury in heart muscle has recently been reported (see E. P. Chen et al., Extracellular superoxide dismutase transgene overexpression preserves post-ischemic myocardial function in isolated murine hearts, Circulation, 94:412-417, 1996, which is incorporated herein by reference). In particular, non-toxic seleno-organic free radical scavengers were found to exhibit such a cytoprotective effect (see V. Ullrich, et al., Seleno-binding equilibria between plasma and target proteins, Biochem. Pharmacol. 52:15, 1996, which is incorporated herein by reference).
Implantation of cells from skeletal muscle origin or of embryonic heart muscle cells (cardiomyocytes) into ischemic or infarcted regions of the heart has recently been reported (see R. K. Li et al., Cardiomyocyte transplantation improves heart function, Ann. Thorac. Surg. 62:454-460, 1996, which is incorporated herein by reference). The implanted cells survived the implantation and remained viable for a period of at least several weeks thereafter. The cells, implanted into a cold injury site of the left ventricle myocardium of rats, were reported to significantly improve the heart function (with respect to various physiological parameters) in comparison with control rats, which had not undergone cells implantation. In experiments on mice performed (see J. E. Morgan et al., Yield of normal muscle from precursor cells implanted into preirradiated and nonirradiated legs of young and old max mice, Muscle and Nerve 19:132-139, 1996, which is incorporated herein by reference), only about 10% of the implanted cells of skeletal muscle origin survived the implantation and remained viable for a period of few weeks after the implantation.
Low power laser irradiation has recently been found to modulate various processes in different biological systems (see M. Belkin, B. Zaturunsky, and M. Schwartz, A critical review of low power laser bioeffects, Laser Light Ophthalmol. 2: 63-71, 1988, and T. Karu, Photobiology of low power laser effects, Health Phys. 56: 691-704, 1988). For example, in isolated mitochondria, Hexe2x80x94Ne laser irradiation (5 J/cm2) elevated membrane potential and production of ATP, while in isolated fibroblasts with the same radiation, an increase in collagen production was observed. The effect of low power laser irradiation on regeneration processes following trauma has thus far been investigated in the skin, the peripheral nervous systems, skeletal muscles and bone. It has been found that laser irradiation given at the right time and energy level modulates the process of skeletal muscle regeneration and, in most systems, causes a faster recovery after trauma and an enhanced rate of regeneration in muscles and bone (see N. Weiss and U. Oron, Enhancement of muscle regeneration in the rat gastrocnemius muscle by low power laser irradiation, Anat. Embryol. 186: 497-503, 1992, and O. Barushka, T. Yaakobi and U. Oron, Effect of laser irradiation on the process of bone repair in the rat tibia, Bone 16: 47-55, 1995). Low power laser irradiation has also been found to induce a twofold increase in new blood vessels formation (i.e., angiogenesis) in the injured zone of skeletal muscles (see A. Bibikova, N. Belkin and U. Oron, Enhancement of angiogenesis in regenerating gastrocnemius muscle of the toad by low energy laser irradiation, Anat. Embryol. 190:597-602, 1994, which is incorporated herein by reference).
In a recent study, the effect of irradiation of the blood (subclavian artery) by Hexe2x80x94Ne lasers in patients after MI was observed (see N. N. Kipshidze et al., Intravascular laser therapy of acute myocardial infarction, Angiology 801-808, September 1990, which is incorporated herein by reference). The study reports a better recovery of the laser-irradiated patients in terms of the levels of enzyme activity (creatine phosphokinase) in blood (which was lower in the irradiated patients) and a reduction of arrhythmia of the heart.
It is to be emphasized that the Kipshidze et al. paper does not teach biostimulation of the myocardium itself but rather of the blood. The authors write in the Abstract xe2x80x9cA new method for . . . using monochromatic Hexe2x80x94Ne laser . . . this paper deals with the effect of endovascular (inside blood vessels) laser blood irradiation on high-grade arrhythmiasxe2x80x9d. On page 802, lines 2-3, it states that xe2x80x9cEndovascular laser therapy was performed using an LG-75 laser via an optical light guide introduced into the lumen of the superior vena cava . . .xe2x80x9d. Thus, the myocardium was not irradiated but rather the blood.
It is known in the art (see Mester, A. R., Modalities of low power laser applications, Galletti et al. (eds.) Laser Applications in Medicine and Surgery, Monduzzi Editore (1992), pp. 33-40) that the energy emitted from a Hexe2x80x94Ne laser, even with high power, is absorbed by hemoglobin in the red blood cells and by living tissues. This type of energy at the specific wavelength (632.2 nm) does not penetrate well through living tissues. The loss in power output is about 90% after 2 mm depth of tissue and there is practically no power capable of penetrating beyond 3 mm depth of tissue with a moderate blood supply. It is also acknowledged in the art that exposure of the tissue to power less than 4 mW has no biostimulatory effect on tissues (see Galletti et al. ibid. and Bradley, P. F. and B. Gursoy, Penetration studies of low intensity laser therapy (LILT) wavelength, Proc. WALT 1996, p. 18.).
Thus, when energy from the Hexe2x80x94Ne laser source (the power level is not cited in the Kipshidze et al. work, but can be at most 40 mW) is conveyed through an optical fiber (which causes a loss of approximately 30-40% of the source), it ends up at the tip of an optical fiber at no more than 25 mW. Since the tip is situated in a blood vessel (superior vena cava) which is at least 5 cm in distance from the heart muscle, the energy which is absorbed by the heart muscle from the optical fiber is practically zero and has no biostimulatory effect on the heart muscle based on the above scientific knowledge.
Other studies have reported qualitative alternations in the ultrastructure of musculature (see Ruzov, I. V. and Baltrushaitis, K. S., Ultrastructural changes in the myocardium under the action of the helium-neon laser and obzidan, Vopr. Kurotol. Fizioter. Lech. Fiz. Kult. 5-6: 62-4, 1992), blood vessels (see Ruzov, I. V. and Baltrushaitis, K. S., The microcirculatory bed of the ischemic myocardium under the combined action of a low-intensity helium-neon laser and finoptin, Vopr. Kurotol. Fizioter. Lech. Fiz. Kult. 4: 31-3, 1993) and mitochondria of the myocardium of rabbits in a hypodynamic stage following irradiation of the blood by Hexe2x80x94Ne laser (see Ruzov, I. V. and Rishkus, L. A., The effect of the helium-neon laser on the cyclic nucleotide level in experimental hypodynamia, Vopr. Kurotol. Fizioter. Lech. Fiz. Kult. 2:51-53, 1992). The irradiation in the above studies was performed by insertion of fiber optics through the ear vein in the ear of the rabbits. It should be emphasized that in the Russian Republic, irradiation of blood by UV or low power lasers is a common procedure towards a better recovery in many human illnesses (see Ruzov, I. V. A comparative study of the action of the helium-neon laser, perlinganite and heparin on the energy apparatus of the ischemic myocardium. Vopr. Lech. Fizioter. Lech. Fiz. Kult. 5-6: 62-4, 1994).
In the four aforementioned scientific papers by Ruzov et al, the authors use an experimental system of Hexe2x80x94Ne laser at a power level of 1.5 mW, similar to Kipshidze et al. Again, the energy was introduced by fiberoptics into a vein in the ear of a rabbit. As mentioned above with reference to the paper by Kipshidze et al., the energy that is finally transmitted from the vein in the ear to the heart muscle is practically zero, without any expected biostimulatory effects on ischemic or hypodynamic heart muscle, as mentioned in these scientific papers.
Russian Patent 1715351 to Golikov et al., relates to irradiation treatment by a Hexe2x80x94Ne laser at acupuncture points to help recovery of heart disease in the post-infarction period. However, this patent can not relate to irradiation of the myocardium because the Hexe2x80x94Ne laser beam, even if aimed at points on the chest of a human patient above the heart, cannot penetrate more than 2-3 mm. Thus, practically no laser energy can reach the heart muscle since the muscle between the ribs in humans is at least 3 cm thick. The positive effects achieved in laser irradiated patients, is perhaps due to acupuncture treatment or reflexogenic therapy, as cited by the authors themselves in the last paragraph of the patent.
Russian patent 1806781 to Leveshunov et al., deals with magnetic-laser treatment to improve clinical prognosis of patients with complicated acute myocardial infarction. Pulsed laser irradiation and infrared radiation (wavelength not mentioned) are applied to the patients"" chest wall. There is no known data in the art on the bioeffects of combination of magnetic field and laser irradiation on tissues. The pulsed laser, as suggested in this patent, has a mean power of 12 mW, while the continuous infrared radiation has a power of 50 mW. However, the laser beam has to penetrate through the chest skin and muscles between the ribs with a total average tissue width of about 3 to 5 cm before reaching the heart muscle. Since the laser power diminishes within living tissue in an exponential manner with respect to depth, the maximal laser power output incident on the heart, as suggested by Leveshunov et al., will be reduced through the thick chest wall of a patient to a practically zero, obviously too low to cause any stimulatory effect on the heart muscle.
The present invention seeks to provide methods and apparatus for improvement of heart function, reduction of scar tissue formation and/or enhancement of the regeneration of myocardial tissue following myocardial infarction, or other heart failure syndromes, by electromagnetic radiation.
Methods in accordance with preferred embodiments of the present invention are based on stimulating myocardial tissue of a patient by irradiation of the tissue with electromagnetic radiation. In the context of the present patent application and in the claims, such methods are referred to as electromagnetic cardiac biostimulation (ECB). ECB in accordance with the principles of the present invention is not limited to any particular range of wavelengths, but the best mode of carrying out the invention is believed to be based on irradiation in the range including infrared (IR), visible light and ultraviolet (UV) radiation. The choice of which particular wavelength, power level, duration of irradiation and number of irradiation sessions is made in accordance with the patient""s needs.
Preferably, the radiation used in ECB is coherent, such-as radiation provided by a laser, but it may alternatively be non-coherent, such as provided by a xenon lamp.
Possible therapeutic effects of biostimulation of infarcted myocardium include a reduction in the size of an infarct, regeneration of cardiomyocytes in the infarct, preservation of the structure and activity of mitochondria in cardiomyocytes, and improved function of diseased myocardium. It is a particular feature of some aspects of the present invention to use electromagnetic radiation to cause regeneration and cytoprotection of cardiomyocytes, following acute ischemia, including preserving the structure and orientation of contractile proteins in the cardiomyocytes, since heretofore, there has been no method known in the art for regeneration and cytoprotection of cardiac muscle under these circumstances. In some preferred embodiments of the present invention, the method of ECB is non-invasive both to the body and to the heart, such as by placing a radiation source against the skin of the patient and irradiating the myocardium therefrom. In other preferred embodiments, some body tissue, such as non-myocardial muscle tissue in the chest or the back of the patient, may be at least partially exposed surgically, and the heart is irradiated therefrom. Although this option is partially invasive to the body, it has the advantage of allowing the radiation to penetrate through a thinner muscle layer, so as to attain a higher, more optimal radiative power on the heart muscle. In still other preferred embodiments, the ECB method may be invasive to the heart, such as by irradiating the heart by means of a catheter introduced into a coronary artery or through a blood vessel into a chamber of the heart.
In some preferred embodiments of the present invention, an ECB method includes a combination of biostimulation by electromagnetic radiation and additional post-infarct clinical treatments, to achieve synergetic effects. Such treatments may include administration of chemical compounds and drugs, such as FDP or non-toxic seleno-organic free radical scavengers, as described above, and laser myocardial revascularization (LMR) procedures, as are known in the art.
LMR is a technique known in the art for creating channels in ischemic heart tissue to improve the blood supply thereto. PCT patent application no. PCT/IL97/00011, filed Jan. 14, 1997, which is assigned to the assignee of the present patent application and incorporated herein by reference, describes LMR in detail. In some preferred embodiments of the present invention, methods and apparatus of LMR described in the PCT/IL97/00011 application are preferably used in conjunction with ECB to effect synergetic healing of ischemic zones of the heart, as described below. The ECB irradiation is preferably performed during a LMR procedure, so as to irradiate the ischemic area and the channels generated therein. The irradiation enhances healing of the channels and ischemic area and stimulates angiogenesis in the vicinity of the LMR channels, as mentioned above (see A. Bibikova et al., 1994).
As descibed above, FDP is believed to partially inhibit (post-infarct) ischemia by re-activating anaerobic glycolysis. It may also alleviate post-reperfusion injury by accelerating the replenishment of high energy metabolites such as ATP and CP. Non-toxic seleno-organic free radical scavengers are also believed to exhibit cytoprotective effects, by inhibiting the toxic effects of reperfusion-generated superoxides, thus alleviating post-reperfusion injury, as mentioned above. Similarly, in accordance with principles of the present invention, low-power laser irradiation of the infarcted zone immediately after acute MI is believed to protect the energy-producing organelles in the cells (mitochondria) from acute damage. Administration of FDP or non-toxic seleno-organic free radical scavengers, which act as cytoprotective agents when delivered to the infarcted area through the blood system, in conjunction with local treatment by ECB, is expected to synergistically intensify healing effects on infarcted myocardial zones. Therefore, in accordance with another preferred embodiment of the present invention, ECB irradiation is performed, preferably closely following the occurrence of an infarct, in conjunction with intravenous administration of exogenous FDP or non-toxic seleno-organic free radical scavengers. The combined effect of the irradiation and the drugs preserves structure and activity of mitochondria in a more effective way.
In some preferred embodiments of the present invention, an ECB device comprises at least one electromagnetic radiation source; relay optics, preferably comprising at least one waveguide, which is coupled to the at least one electromagnetic radiation source; and a lens, for directing radiation from the waveguide onto heart tissue. Preferably, the ECB device further comprises a position sensor, which facilitates the positioning of the waveguide and lens, and a control unit which controls the various functions of the ECB device, including modulation of the source output power and spectrum, duration of the irradiation and positioning. Preferably, the ECB device comprises a visible light source and a light guide optically coupled thereto, preferably a fiberoptic light guide, for the observation of the irradiating during some ECB procedures.
In accordance with a preferred embodiment of the present invention, the at least one electromagnetic radiation source comprises a source of coherent light. The source of coherent light may include a diode laser. Preferably, the diode laser has a power output in the range of 5 mW to 5 W and a wavelength in the range of 250 to 940 nm.
Alternatively, electromagnetic radiation source comprises a source of non-coherent light, preferably, a high intensity xenon lamp. Preferably, the xenon lamp has a power flux of 30 to 500 mW/cm2.
In preferred embodiments of the present invention, the relay optics and position sensor are contained within a catheter for introduction into a chamber of the heart or into a coronary artery for intracardiac irradiation. Most preferably, the catheter is disposable and comprises at least one waveguide, a lens, and a position sensor, for example a magnetic position sensor, as described in PCT patent publication number WO96/05768, which is incorporated herein by reference, to enable navigation and location of the catheter following a viability map, as described below.
In further preferred embodiments of the present invention, the catheter comprises a sensor for determining viability or non-viability of the myocardial tissue. Such sensors may comprise one or more electro- or mechano-physiological detectors, which sense local myocardial electrical or mechanical activity, respectively, as described, for example, in U.S. patent application Ser. No. 08/595,365, which is assigned to the assignee of the present patent application, and in U.S. Pat. No. 5,568,809, both of which are incorporated herein by reference. The viability data gathered in conjunction with location coordinates is used to generate a viability map on which the ischemic regions to be irradiated are identified.
Alternatively or additionally, such sensors may also be used post-irradiation to assess irradiation efficacy in promoting preservation of the heart muscle following ischemic damage. Optionally, the detectors may be used in between ECB sessions to assess efficacy and/or to update the viability map.
Blood and muscular tissue have very high extinction coefficients with respect to biostimulatory electromagnetic radiation wavelengths. Hence, biostimulatory radiation has to be applied in close proximity to, and preferably in contact with, the target area. Accordingly, in some preferred embodiments of the present invention, the catheter comprises one or more proximity or contact sensors, known in the art, for sensing and assuring contact between the catheter and the wall of the heart chamber.
In alternative preferred embodiments of the present invention, mainly those employing non-invasive ECB methods, the ECB apparatus is used in conjunction with an echo ultrasound transducer which communicates with an echo imaging device. The echo transducer provides positional information regarding the infarct and facilitates aiming the irradiating optics to the infarcted heart zones during irradiation. Most preferably, the echo transducer is fastened to the electromagnetic radiation optics, so as to substantially maintain them in a fixed spatial relationship with each other.
In some preferred embodiments of the present invention, the ECB apparatus is adapted to operate in conjunction with LMR procedures, for example those described in PCT application IL97/00011, mentioned above. Accordingly, an integrated catheter, which is adapted for the combined operation, comprises at least one waveguide coupled to the LMR laser source, at least one waveguide coupled to the ECB electromagnetic radiation source, suitable optics, at least one position sensor and, optionally, at least one physiological detector, such as an electrode, for sensing physiological activity in the heart muscle.
Typically, ischemic zones in the myocardium may comprise up to 10 cm2 in area, whereas the typical cross section of an intracardiac catheter is several mm2. Moreover, as noted above, biostimulatory wavelengths do not penetrate substantially more than a few millimeters through blood or muscular tissue. The steep decay of power level restricts the maximal distance between the radiation emitting area and the target area and/or the minimal allowable electromagnetic radiation source power output. Employing a small radiation emitting area for the irradiation of a significantly larger target makes the procedure tedious and time-consuming.
Accordingly, it is an object of some aspects of the present invention to provide radiation-conveying catheters, which spread the radiation over an extended target area, preferably an area larger than a cross-section of the catheter itself, while still enabling efficient energy transfer from the catheter to the tissue. In some preferred embodiments of the present invention, an ECB catheter, for invasive irradiation of the heart, comprises a wide angle lens, for example, a fish-eye lens, as is known in the art, to widen the irradiation beam, at the distal end of the catheter. Alternatively, the widening of the radiation emitting area is achieved by employing a side-emitting or widening optical tip catheter, as described below. Preferably, the optics in the catheter are designed to provide a generally uniform level of irradiation over as substantial portion of the target area.
In some preferred embodiments of the present invention, a side-emitting ECB catheter comprises a longitudinally-disposed radiation-emitting element, for example, a window or lens, for delivering radiation in a radial direction over a substantial portion of the length of the catheter adjacent a distal end thereof. The radiation-emitting element is coupled to the waveguide, which transmits the radiation from the electromagnetic radiation source, and is preferably fitted in a slot or cutaway section along the distal portion of the catheter. Most preferably, the radiation-emitting element is 2 to 3 cm long and 0.2 to 0.3 cm wide, forming a radiation emitting area of approximately 0.5 cm2. Optionally, it has a curved outer surface, which further increases the effective area of irradiation of the element.
As mentioned above, the radiation-emitting element is preferably brought into close proximity to or contact with the target area. Accordingly, in some of these preferred embodiments, the distal portion of the side-emitting catheter is designed to conform to the inner surface of the heart wall when pressed thereagainst, as described in U.S. Provisional Patent Application 60/034,704, which is assigned to the assignee of the present application and incorporated herein by reference. Preferably, as described in the 60/034,704 application, the catheter includes one or more position sensors and/or pressure or proximity sensors, which are used to ascertain the position and orientation of the radiation-emitting element against the heart wall during irradiation.
Alternatively, the catheter may comprise a slanted tip, including a generally elliptical radiation-emitting area, angled with respect to the catheter""s longitudinal axis. Preferably, the elliptical area has an outwardly curved surface, for further increasing the effective irradiation area, as described above.
In alternative preferred embodiments of the present invention, the catheter comprises a widening optical tip, which is maintained in a narrow configuration during insertion into the body, but then stretches open after insertion, so as to considerably increase the tip area that is brought into contact with and irradiates the heart tissue. Such a tip may comprise, for example, a fiberoptic bundle, or a radiation-reflecting surface, such as foldable parabolic or multifaceted reflector, surrounding a point-like radiation source, such as the distal tip of the waveguide. Optionally, the widening tip may comprise an optical membrane, as for example a scattering membrane, a layered polarizer membrane, translucent membrane or any other suitable optical membrane known in the art, to spread and/or diffuse the radiation emitted by the waveguide.
In some alternative preferred embodiments of the present invention, the catheter comprises a radiometric sensor, which is placed in or against myocardial tissue to be irradiated so as to measure the local instant radiation power level incident on the tissue and the total irradiative energy supplied to the tissue during an ECB session. The power and the energy level readings may be employed for modulation of the ECB source output power level and for determination of a session""s duration. Optionally, the readings may serve to ascertain successful transmission of the ECB radiation from the source through the relay optics and to the designated heart tissue area.
Intravascular irradiation of the blood using a 5 to 50 mW Hexe2x80x94Ne laser has been shown to improve heart function (see N. N. Kipshidze, mentioned above). It is believed by the inventors of the present patent application that the Hexe2x80x94Ne laser irradiation may also have a beneficial effect on the atherosclerotic process in coronary arteries, and the combination of such irradiation with biostimulatory irradiation of ischemic zones may prove synergistically beneficial to the heart function following acute myocardial infarct. Accordingly, in alternative embodiments of the present invention, an ECB method includes a combination of ECB irradiation and additional intravascular Hexe2x80x94Ne irradiation of the blood.
In alternative embodiments of the present invention, an ECB method includes in vitro ECB irradiation of cells taken from skeletal muscle or embryonic heart muscle (cardiomyocytes) prior to their implantation into ischemic areas of the heart muscle, in accordance with the methods described by Li and Morgan, cited above. The applicants believe that such biostimulatory irradiation of the cells may improve their overall viability and increase their implant survival rate due to the beneficial effects of the biostimulatory irradiation with respect to cell preservation under ischemic conditions. As described by Li and Morgan, such viable implanted cells are believed to improve the heart function.
There is thus provided in accordance with a preferred embodiment of the present invention, a method for biostimulation of a myocardial tissue including irradiating the myocardial tissue with a source of electromagnetic radiation which causes biostimulation of the myocardial tissue.
Preferably, the electromagnetic radiation is selected from the group consisting of infrared, visible light and ultraviolet radiation.
Preferably, irradiating the tissue includes irradiating after the myocardial tissue develops an infarct of a given size, such that irradiating the myocardial tissue causes a reduction in the size of the infarct, and/or such that irradiating the myocardial tissue causes regeneration of cardiomyocytes in the infarct, and/or such that irradiating the myocardial tissue preserves structure and activity of mitochondria in cardiomyocytes in the infarct, and/or such that irradiating the myocardial tissue preserves structure and activity of contractile proteins in cardiomyocytes in the infarct.
Preferably, the source of electromagnetic radiation includes a source of coherent light, most preferably a diode laser having a power output in the range of 5 mW-5 W and a wavelength in the range of 250-940 nm.
Preferably, irradiating the tissue includes a plurality of irradiations of the myocardial tissue with the source of electromagnetic radiation and/or irradiating myocardial tissue with the source of electromagnetic radiation for a duration of 0.5-15 minutes.
In a preferred embodiment of the invention, irradiating the tissue includes introducing a catheter into the heart, preferably through the aorta, positioning the catheter in proximity to a heart wall, and irradiating the myocardial tissue via a waveguide introduced by the catheter into the heart, wherein the waveguide is coupled to the source of radiation.
In another preferred embodiment, a therapeutic chemical compound is administered in conjunction with the irradiating. Preferably, the chemical compound includes administering fructose-1,6-diphosphate (FDP), or alternatively, a seleno-organic free radicals scavenger. Preferably, irradiating the tissue and administering the chemical alleviate a post-reperfusion injury.
In still another preferred embodiment, a myocardial revascularization procedure in conjunction with the irradiating, wherein performing the myocardial revascularization procedure preferably includes performing a revascularization procedure simultaneously with the irradiating.
Preferably, physiological signals are received from the tissue, wherein irradiating the tissue includes irradiating heart tissue in response to the signals received therefrom. Preferably, the physiological signals include mechano-physiological signals and/or electrophysiological signals.
Preferably, positioning the catheter includes tracking location coordinates of the catheter using one or more position sensors. Further preferably, positioning the catheter includes positioning the catheter responsive to a viability map, which indicates ischemic areas in the heart tissue. Alternatively or additionally, positioning the catheter includes positioning the catheter relative to a grid delineating a zone to be irradiated on a geometrical map of the heart and, preferably, marking irradiated locations on the grid.
Preferably, irradiating the tissue includes simultaneously irradiating an area of the heart wall substantially larger than a cross-sectional area of the waveguide.
In a preferred embodiment of the invention, irradiating the tissue via the waveguide includes expanding a radial dimension of the waveguide adjacent the tissue.
In another preferred embodiment, positioning the catheter includes pressing a flexible distal portion of the catheter against the heart wall so that the portion conforms to the wall, and wherein irradiating the tissue includes irradiating an area radially adjacent the distal portion. Preferably, irradiating the tissue includes irradiating a first elongate stripe on the heart wall adjacent the distal portion in a first position thereof, and irradiating a plurality of stripes generally parallel to the first stripe.
In still another preferred embodiment, the catheter is introduced into a coronary artery.
In yet another preferred embodiment, irradiating the heart tissue includes irradiating the heart epicardially, in addition to or instead of irradiating via the waveguide introduced by the catheter.
Preferably, non-myocardial tissues are at least partially exposed in a generally perpendicular direction to a lateral wall of the myocardial tissue, and irradiating the tissue includes placing an optical element coupled to the source of electromagnetic radiation onto the at least partially exposed non-myocardial tissues. Preferably, the non-myocardial tissues include chest muscles of a chest cavity and irradiating the tissue includes placing the optical element into the chest cavity in a vicinity of the tissue, most preferably in proximity with the pleural membrane.
In a preferred embodiment of the invention, the source of electromagnetic radiation includes a source of concentrated non-coherent light, preferably a xenon lamp, most preferably having an radiative power flux of 30-500 mW/cm2.
There is further provided, in accordance with a preferred embodiment of the present invention, apparatus for biostimulation of myocardial tissue including:
a source of electromagnetic radiation; and
relay optics, which receive the electromagnetic radiation, and convey the radiation to irradiate an ischemic area of the myocardial tissue.
In a preferred embodiment of the invention, the apparatus includes an echo transducer which communicates with an echo imaging device, the echo transducer being operative to provide positional information of the infarct; and a fastener which fastens the relay optics together with the echo transducer and which substantially maintains the two in a fixed spatial relationship with each other.
Preferably, the electromagnetic radiation source includes a coherent source, most preferably a diode laser having a power output in the range of 5 mW to 5 W and a wavelength in the range of 250 to 940 nm.
Alternatively, the electromagnetic radiation source includes a non-coherent source, preferably a xenon lamp having a radiative power flux of 30 to 500 mW/cm2.
In a preferred embodiment of the invention, the apparatus includes a moving arm which holds the relay optics and a servo unit for controllably moving the arm.
Preferably, the relay optics include a fiberoptic light guide, having a distal end for introduction into a patient""s chest, and a proximal end communicating with the electromagnetic radiation source. Preferably, the optics include a filter to attenuate electromagnetic radiation power output therefrom and a lens coupled to the distal end of the fiberoptic light guide.
In a preferred embodiment of the invention, the apparatus includes an elongate probe for introduction into a heart chamber, wherein the relay optics include a waveguide contained within the probe.
Preferably, the probe includes at least one position sensor, which is used to locate the probe within the chamber of the heart, wherein the position sensor preferably includes a magnetic position sensor, which generates signals responsive to an external magnetic field.
Additionally or alternatively, the probe includes at least one physiological sensor for sensing local physiological signals from the heart indicative of myocardial viability.
Further additionally or alternatively, the probe includes a radiometric sensor for sensing a local electromagnetic radiation power level reaching the myocardial tissue.
In a preferred embodiment of the invention, the probe includes a LMR waveguide, which communicates with a laser source for laser revascularization of the myocardial tissue. Preferably, the LMR waveguide is connected at its distal end to a lens adapted to concentrate the laser beam onto the tissue.
Preferably, the waveguide includes fiberoptics and is connected at a distal end thereof to an optical element, which spreads the biostimulatory electromagnetic radiation. Preferably, the optical element includes a wide-angle lens, most preferably a fish-eye lens. Preferably, the optical element emits a beam having a cross-sectional area substantially larger than a cross-section of the waveguide.
There is also provided, in accordance with a preferred embodiment of the present invention, apparatus for intracardiac irradiation, including:
an elongate probe having a proximal end and a distal end for insertion into the heart of a subject, and including:
a waveguide, which conveys electromagnetic radiation from a source at the proximal end to the distal end; and
an optical element adjacent to the distal end, which receives electromagnetic radiation through the waveguide and emits a beam having a cross-sectional area substantially larger than a cross-section of the waveguide.
Preferably, the optical element includes an elongate, longitudinally-disposed element, which emits the beam in an outward radial direction relative to the probe.
Preferably, the optical element includes a curved outer surface and is at least 2 cm long and between 2 and 3 mm wide.
In a preferred embodiment of the invention, the probe includes a flexible portion, which contains the optical element, and which conforms to a wall of the heart such that the optical element is in physical contact therewith, wherein the probe preferably includes two or more proximity sensors, most preferably pressure sensors, which sense a contact of the probe with the heart wall.
In another preferred embodiment; the optical element includes a generally elliptical radiation-emitting area at the distal end of the probe, obliquely disposed with respect to the probe""s longitudinal axis, wherein the element preferably has a convex outer surface.
In yet another preferred embodiment, the optical element includes a widening optical tip at the distal end, having a narrow, closed configuration for insertion into the heart and a wide, expanded configuration for irradiation of the myocardial tissue inside the heart.
Preferably, the tip includes a radiation scattering membrane. Alternatively or additionally, the tip includes a foldable reflector encompassing a radiation emitting point source, wherein the reflector preferably includes a multifaceted reflector.
Further alternatively, the tip includes a foldable fiberoptic bundle.
In a preferred embodiment of the invention, the probe includes an external sleeve and an internal sleeve, slideable within the external sleeve, wherein the internal sleeve includes a stretchable portion adjacent the distal end of the probe, which is held within the external sleeve in the closed configuration, and which stretches open when the internal sleeve is slid distally out of the external sleeve in the open configuration.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: